U.S. Pat. No. 3,936,776 to John Robert Sundquist shows a helical resonator filter with a conductor having two tightly-coupled portions of like pitch and interspersed turns and a pair of respective opposite ends of the portions being connected directly to the shield or cavity of the individual resonator. The resonator described in this patent provides odd harmonic suppression. However, the relative positions of the two interspersed coils is believed to be somewhat critical, thus rendering the resonator difficult to construct. In addition, this type of resonator has a reduced tuning range because of the capacitive coupling between its windings.